1. Field of the Invention
The present invention relates to methods for manufacturing organic-inorganic composite particles, an optical material, an optical element and a lens, and to an organic-inorganic composite particles.
2. Description of the Related Art
Glass used as optical materials for lenses and other optical elements has been being replaced with organic polymers. Among such organic polymers, cyclic olefin polymers are superior in transparency, low water absorption and moldability, and are widely used as optical materials accordingly.
Optical materials are widely used in the field of optical elements used in various optical apparatuses, such as cameras including still cameras and video cameras, optical pickup devices for CDs, MOs, DVDs and other optical media, and office automation apparatuses including copy machines and printers. Such an optical material is required to have superior optical characteristics, such as high light transmittance and high refractive index, high stability in refractive index to temperature, low coefficient of linear expansion, high thermal stability, high hardness, low water absorption, high weather resistance, high solvent resistance, and so forth.
However, it is difficult to enhance these characteristics significantly only by use of cyclic olefin polymers. In order to solve these issues, it has been proposed to enhance various characteristics of optical material by dispersing inorganic particles in a cyclic olefin polymer. In this instance, the inorganic particles are each coated with a surface modifier to prevent the aggregation of the particles.
Japanese Patent Laid-Open No. 2006-161000 discloses a method for enhancing the dispersibility of inorganic particles in thermoplastic resins such as cyclic olefin polymers by modifying the surfaces of the inorganic particles with a silane coupling agent such as tetramethoxysilane. Japanese Patent Laid-Open No. 2007-238930 discloses a method for manufacturing a molded lens by heating and compressing an organic-inorganic composite composition prepared by mixing inorganic particles and a thermoplastic resin having a functional group capable of forming chemical bonds with the inorganic particles, such as a cyclic olefin polymer.
In the method disclosed in Japanese Patent Laid-Open No. 2006-161000, however, only a silane coupling agent is used to enhance the dispersibility. Consequently, some characteristics such as coefficient of linear expansion and heat resistance may be degraded.
In the method disclosed in Japanese Patent Laid-Open No. 2007-238930, since the functional group is chemically bound to inorganic particles not surface-modified, the inorganic particles may undesirably aggregate to increase the particle size.